Effects of ammonium to nitrate ratio on growth, nitrogen metabolism, photosynthetic efficiency and bioactive phytochemical production of Prunella vulgaris

Abstract

Context: Prunella vulgaris L (Labiatae) is commonly used as a traditional medicinal herb in some Asian and Europe countries. To date, few studies have been conducted to determine the influence of − N/ − N ratio on growth, physiological development, and bioactive phytochemical accumulation in hydroponically grown P. vulgaris.Objective: The current study was conducted to evaluate the effect of five − N/ − N ratios on growth, nitrogen metabolism, photosynthetic efficiency, and bioactive phytochemical production in P. vulgaris.Materials and methods: Hydroponically cultivated P. vulgaris were fertilized with five − N/ − N ratios in a greenhouse for 85 d. Dried weight of root, stem, leaf and spica, leaf area, photosynthetic efficiency, activities of nitrate reductase (NR), glutamine synthetase (GS), and the concentrations of N, soluble protein, and free amino acids in the leaves, as well as the contents of rosmarinic acid (RA), ursolic acid (UA), and oleanolic acid (OA) in the spicas were measured.Results: Both − N and − N as the sole source of nitrogen had inhibitory effects on P. vulgaris growth. P. vulgaris fertilized with the 25/75 ( − N/NO3 − N) ratio had the highest leaf area, photosynthetic rate, and chlorophyll content. The 25/75 (/) ratio increased the spica biomass by 1828%, nitrate-reductase (NR) activity by 98%, and soluble protein concentration by 29.45% compared with the 100/0 (/) treatment. Additionally, 25 − N/75 NO3 − N resulted in the highest contents of RA and total flavonoids as well as relatively high contents of UA and OA; therefore, this ratio had the highest yield of RA, UA, OA, and total flavonoids in spicas.Discussion and conclusion: The use of 25 − N/75 − N is recommended to improve biomass production and medicinal quality of P. vulgaris.